Method of MAG arc welding and welding apparatus

Abstract

An MAG arc welding method and apparatus is capable of achieving a welding bead in a regular ripple pattern or in a suitable sectional form. The welding power source generates the first welding current I1 and a second welding current I2 larger than the first welding current. The wire melting speed is changed by switching between the first and the second welding currents. The welding method or apparatus according to the invention generates the first arc length more than 2 mm and the second arc length more than the first arc length and switches between both arc length at a switching frequency F of 0.5 to 25 Hz. The ratio of the second to the first welding currents is made to be in 1.03 to 1.20. In addition to a welding method to change the arc length by switching the first and the second welding currents at a constant wire feeding rate, the present welding method makes it possible to carry out the lap welding or butt welding even when there is a large gap. The large gap requires a large amount of molten metal which is prepared by increasing the wire melting speed caused by an increase in the wire feeding rate by 5 to 20%. The resultant reinforcement has a beautiful appearance.

We claim: 
     
       1. A pulse MAG arc welding apparatus for carrying out an arc welding operation by supplying a pulse welding current while switching the same between a first pulse current group for generating a short arc length and a second pulse current group for generating a long arc length, said apparatus comprising: an arc voltage detection circuit for detecting an arc voltage value and outputting an arc voltage detection signal corresponding thereto;   an arc voltage setting circuit for setting a value of arc voltage in according with welding conditions and outputting an arc voltage setting signal corresponding thereto;   a comparison circuit for comparing said arc voltage detection signal and arc voltage setting signal and outputting a difference between said two signals as an arc voltage control signal;   a pulse condition control signal generation circuit for generating a pulse condition control reference signal for controlling one preselected among four pulse control conditions in common with said first and second pulse current groups in accordance with said arc voltage control signal, said four pulse control conditions comprising pulse frequency, pulse width, base current value and peak current value;   a first pulse current setting circuit for setting remaining three pulse control conditions for said first pulse current group which have not been preselected and for outputting first pulse current group setting signals including setting signals corresponding to said remaining three pulse control conditions other than said pulse condition control signal;   a second pulse current setting circuit for setting remaining three pulse control conditions for said second pulse current group which have not been preselected and for outputting second pulse current group setting signals including setting signals corresponding to said remaining said three pulse control conditions other than said pulse condition control signal;   a switching circuit for generating a switching signal for switching said first and second pulse current setting circuits alternatively at a frequency ranging from 0.5 to 25 Hz;   a pulse frequency signal generation circuit for generating a pulse frequency signal in response to either the pulse frequency control reference signal if output from said pulse condition control signal generation circuit, or, the pulse frequency setting signal output alternatively from selected each of said first and second pulse current setting circuits if said pulse frequency control signal is not output from said pulse condition control signal generation circuit;   a pulse frequency and width signal generation circuit for outputting a pulse frequency and width signal in response to   the pulse frequency control signal and pulse width setting signal if the pulse frequency control reference signal is output from said pulse condition control signal generation circuit,   the pulse frequency signal and pulse width control signal if the pulse width control signal is output from said pulse condition control signal generation circuit, or   the pulse frequency signal and pulse width setting signal if the peak current control signal or base current control signal is output from said pulse condition control signal generation circuit;   a pulse current control circuit for outputting first pulse control signal and second pulse control signal alternatively in response to   the pulse frequency and width signal, the peak current setting signal and base current setting signal if the pulse frequency control reference signal or the pulse width control signal is output from said pulse condition control signal generation circuit,   the pulse frequency and width signal, the peak current control signal and base current setting signal if the peak current control signal is output from said pulse condition control signal generation circuit, or   the pulse frequency and width signal, the peak current setting signal and base current control signal if the base current control signal is output from said pulse condition control signal generation circuit; and,   a welding power source control circuit for outputting the first pulse current group when the first pulse control signal is output from said pulse current control circuit and the second pulse current group when the second pulse control signal is output from said pulse current control circuit.   
     
     
       2. The pulse MAG arc welding apparatus according to claim 1 wherein said pulse condition control signal generation circuit generates a pulse frequency control signal for controlling the pulse frequency in common with said first and second pulse current groups as said pulse condition control signal and said pulse frequency signal generation circuit generates a pulse frequency signal in response to said pulse frequency control signal input thereto. 
     
     
       3. The pulse MAG arc welding apparatus according to claim 1 wherein said pulse condition control signal generation circuit generates a pulse width control signal for controlling the pulse width in common with said first and second pulse current groups as said pulse condition control signal and said pulse frequency and width signal generation circuit outputs a pulse frequency and width signal in response to said pulse frequency signal from said pulse frequency signal generation circuit and said pulse width control signal from said pulse condition control signal generation circuit. 
     
     
       4. The pulse MAG arc welding apparatus according to claim 1 wherein said pulse condition control signal generation circuit generates a peak current value control signal for controlling the peak current value in common with said first and second pulse current groups as said pulse condition control signal. 
     
     
       5. The pulse MAG arc welding apparatus according to claim 1 wherein said pulse condition control signal generation circuit generates a base current value control signal for controlling the base current in common with said first and second pulse current groups as said pulse condition control signal.